1. Field of the Invention
The present invention generally relates to improving the display of a projected two-dimensional image, especially a color image.
2. Description of the Related Art
It is generally known to project a two-dimensional image on a screen based on a pair of scan mirrors which oscillate in mutually orthogonal directions to scan one or more laser beams over a raster pattern. One scan mirror is typically sinusoidally driven along a horizontal direction at a fast rate of speed, and the other scan mirror is typically linearly driven along a vertical direction at a slower rate of speed. The raster pattern thus created is a series of slanted scan lines resembling a sawtooth pattern. The odd numbered lines in the series generally slope downwardly from left to right across the display, and the even numbered lines in the series generally slope downwardly from right to left across the display. In the middle of the display, the scan lines are equally spaced, and the image is undistorted. However, at the right and left end regions of the display, the scan lines are bunched together in pairs of odd and even numbered lines, thereby making for a distorted image at the end regions of the display.
When only the odd numbered lines, or only the even numbered lines, are used to display a pattern (known as a single-line grating pattern), then the image is displayed reasonably well, although at the expense of resolution and brightness. However, when both the odd numbered lines and the even numbered lines are used to display a pattern (known as a double-line grating pattern), then the image is distorted at the end regions of the display. The problem is particularly noticeable when text is displayed, as well as in images projected in color from a plurality of lasers of different wavelengths. Mechanical misalignment among the laser beams from the lasers leads to color misalignment in the displayed image.